1. Technical Field of the Invention
The present invention relates to a method for manufacturing a coil for a stator loaded on a rotary electric machine, and in particular, to a method for manufacturing a coil called a stator coil wound about such a stator.
2. Related Art
In recent years, small size, high power and high quality have been demanded of rotary electric machines, such as electric motors and electric generators. Taking rotary electric machines loaded on vehicles as an example, the space for loading such a rotary electric machine has been reduced more and more, while the output has been required to be more enhanced.
Under such circumstances, rotary electric machines that have been known include one which is provided with a stator having a stator coil formed of continuous windings, as disclosed in Japanese Patent Laid-Open Publication Nos. 2002-176752 and 2004-320886.
An example of a method for manufacturing a stator coil consisting of continuous windings is provided below.
First, a plurality of shaped wire members are produced from electrically conductive wires, in each of which a plurality of linear portions are juxtaposed being connected with each other via a plurality of turn portions. Each of the turn portions has a staircase portion that has been bent into a staircase shape by plastic deformation. In each staircase portion, the stair case shape is provided toward the linear portions connected by the turn portion. These shaped wire members are integrated with each other to provide an integrated body. In each pair of shaped wire members consisting the integrated body, the plurality of linear portions of one shaped wire member are superposed on the respective plurality of linear portions of the other shaped wire member to form a plurality of linear superposition portions in the longitudinal direction of the integrated body. Thus, the plurality of linear superposition portions are juxtaposed in the integrated body, in the longitudinal direction of the integrated body. The turn portions in the integrated body are curved using plastic deformation so as to have a predetermined winding radius, while the integrated body is wound up by a predetermined number of turns about a core member to form a wound body. In the wound body, the plurality of linear superposition portions in each pair of shaped wire members are radially stacked to form a plurality of linear stack portions in the circumferential direction.
The wound body obtained in this way is disposed in a stator core so that the linear stack portions are located in respective slots of the stator core, with the turn portions being disposed outside the slots, to thereby provide a stator coil.
However, the above manufacturing method causes a difficulty, as explained blow, in winding up the integrated body about the core member with the predetermined winding radius.
Specifically, in the integrated body, each pair of the shaped wire members constructing the integrated body are superposed with each other at the turn portions. Also, the turn portions in each pair of the shaped wire members are each bent into a staircase shape toward the linear portions. Since the turn portions bent into the staircase shape are work-hardened due to the plastic deformation, further plastic deformation of the turn portions is difficult by that much corresponding to the degree of the work hardening. Therefore, it is difficult to reliably wind up the integrated body about a core member, while bending the turn portions so as to have the predetermined winding radius, using plastic deformation. Moreover, the fact that the shape of each turn portion is complicated by the presence of the staircase portion makes it more difficult for the integrated body to be wound up about the core member.
For this reason, the wound body is likely to suffer from a larger winding radius than a desired dimension, from disarray in the staircase portions in the turn portions, from uneven intervals between adjacent linear stack portions, or from misalignment in the plurality of linear superposition portions in the respective linear stack portions. When the linear stack portions of such a stator coil are arranged in the respective slots of the stator core, the accuracy may be deteriorated in the alignment of the linear portions in each slot, the intervals (pitch) may become uneven between the linear stack portions in adjacent slots, or the turn portions projected from the end faces of the stator core are likely to interfere with each other. The deterioration in the alignment accuracy of the linear portions, or the uneven pitch may lead to the deterioration in the slot occupancy in the stator, or to the deterioration in the output of the rotary electric machine using the stator. In addition, the interference between the turn portions may lead to the increase in the size of the stator.